The present invention relates to improvements in a driving power transfer apparatus for a vehicle, and more particularly to a case structure for covering parts of a driving power transfer apparatus.
Japanese Patent Provisional Publication No. 62-275841 discloses a conventional driving power transfer apparatus which is installed in a four wheel drive vehicle equipped with a transverse engine. The driving power transfer apparatus includes a transmission connected to an end side of the engine and a transfer connected to the transmission generally in parallel. The transfer has a center differential, a front differential, a direction changing mechanism and a viscous coupling. A housing of the transfer is constituted by first and second cases. The first case has a large opening so that the ring gear is easily installed in the housing. A flange portion is formed around a peripheral portion defining the large opening of the first case. The flange portion projects outwardly and is connected with a flange portion of the second case by means of bolts. However, since the transfer is located in the vicinity of the engine and has the projecting flange portions, a clearance between the transfer and the engine is small. This limits the arrangement of the engine in an engine compartment of an automotive vehicle.
Further, when the driving torque from the engine is transferred to the direction changing mechanism through the center differential and the front differential, a drive pinion gear of the direction changing mechanism applies a reaction force to the ring gear of the front differential so as to push the ring gear in the lateral direction of the vehicle. The lateral directional reaction force functions so as to increase the clearance between the first and second flange portions. This may degrade the sealing performance of the transfer.